The present invention relates to the protection of pressure vessel walls during thermal transients, and more particularly to a novel construction and arrangement of a thermal sleeve positioned in a pressure vessel nozzle.
Thermal sleeves are generally well known and are highly desirable for use in pressure vessel nozzles for protection of the pressure vessel during temperature changes of the fluid flowing to the vessel. Heretofore, thermal sleeves have usually been formed integral with or welded to the pressure vessel nozzle. Such construction gives rise to high cyclic stresses around the sleeve and nozzle juncture due to mutual restraint of the sleeve and nozzle during temperature transients. This is true even though only one end of the sleeve is attached to the nozzle. Any looseness in the sleeve to nozzle connection allows a flow of fluid to pass between the sleeve and nozzle thereby defeating the desired thermal protection with respect to the nozzle and pressure vessel wall. Other types of devices have been used where the junction between the sleeve and nozzle has been attained by mechanical arrangements, for example, by spring loading as in U.S. Pat. No. 3,232,643. Such arrangements have been generally satisfactory, but are expensive and difficult to fabricate.